In garment production, reinforcing materials are often glued to the back of a fabric to improve its strength or increase its thickness. The reinforcing materials or "fusible interlining fabrics" are coated with an adhesive, and are adhered to another piece of fabric by use of heat and/or pressure.
Fusible interlining fabrics are generally formed of a backing fabric covered with a thermo-adhesive product. The properties of the reinforcing cloth will vary depending on the desired use, and can be woven, knitted, or non-woven fabrics made of natural, synthetic, or metallic materials.
The thermo-adhesive resin is frequently applied to the backing fabric or cloth in a discontinuous pattern, such as a dot pattern applied with an engraving cylinder. The thermo-adhesive, usually in the form of a polymeric powder or paste, is raised to a temperature of about 80.degree. C., at which point it becomes tacky and will stick to the backing. The application of a thermo-adhesive to a backing fabric can also be carried out by a transfer process. In a transfer process, a thermo-adhesive powder is deposited in a dot pattern on a non-adhesive mat, and heated. The fused or melted dots of thermo-adhesive on the non-adhesive mat are then transferred to a backing fabric at a lower temperature. Depositing the thermo-adhesive on a textile substrate by the transfer process makes it possible to avoid excessive penetration of the adhesive into a textile substrate. The resulting thermo-adhesive textile product is then stored at ambient temperature. Preferably the thermo-adhesive textile product will not be tacky or adhesive at ambient temperatures, so that layers of the thermo-adhesive textile product will not adhere to other layers of thermo-adhesive textile product or to other fabrics or materials. Therefore, it is desirable that the resin not become adhesive at too low a temperature, or the product will adhere to other materials at undesired times and locations.
The thermo-adhesive textile product is then used by garment manufacturers who glue the reinforcing material to fabrics by using presses operated at temperatures between 120.degree. C. and 180.degree. C. and at pressures between a few decibars and a few bars for relatively short periods of time (e.g., 10-30 seconds). Under heat and pressure, the polymers and the thermo-adhesive layer (dots) become adhesive. However, if the viscosity of the thermo-adhesive becomes too low, the thermo-adhesive will penetrate completely through the backing fabric or completely through the cloth forming the garment, causing visible marks on the garment cloth or causing undesirable stiffness, which make the product obtained useless. Thus, it is desirable to avoid the use of thermo-adhesive materials which have a viscosity low enough to penetrate completely through either the backing fabric or the garment fabric in order to avoid visible marks on the garment exterior fabric or an undesirable stiffness.
Reinforced fabrics and garments using thermo-adhesive textile products as reinforcing material should also be able to withstand the rigors of normal use and washing; in other words, the bond between the backing fabric and the fabric being reinforced should not break under rigorous ambient conditions caused by use, washing, or dry cleaning.
In order to produce a thermo-adhesive textile product which forms a strong bond capable of withstanding normal use and washing, yet which has sufficient viscosity so as to not penetrate through the backing fabric or the fabric forming the garment, it has been suggested to form the adhesive of two or more layers of polymers with different physical characteristics. By carefully selecting the viscosity and the fusion temperature of these various layers, it is believed possible to limit the excessive penetration of the polymeric adhesive through the backing and/or fabric forming the garment. However, this technique is extremely difficult to perform, and the adhesive remains thermoplastic, so high temperatures during laundering can break the bonds between pieces of fabric.
It has also been suggested to make the resin thermo-setting and thermo-plastic, but it is difficult to control the cross-linking of thermo-setting resins so that the resin will not cross-link before the thermo-plastic material has been heated sufficiently to adhere the thermo-adhesive cross-linkable textile product to another piece of fabric. Further, premature thermo-setting can prevent the thermo-adhesive from being sufficiently thermo-adhesive for application to a cloth or fabric used in a garment.
Therefore, it has been suggested that a thermo-adhesive product should be deposited on a textile substrate, and made thermo-setting by later contact with a cross-linking agent in order to avoid the possibility of thermo-setting the adhesive upon application of the adhesive to the backing or reinforcing material. However, this method does not provide cross-linking throughout the thermo-adhesive material, requires an additional step in garment manufacture, and the addition of cross-linking agent after bonding the reinforcing material to a second piece of fabric is difficult or impossible. Thus, in order to strengthen the bond between the backing or reinforcing textile and the cloth forming the garment by thermo-setting the adhesive, so that, upon heating, the thermo-adhesive does not melt or soften sufficiently to break the bond between the reinforcement and the garment fabric, it was believed necessary to cross-link the adhesive polymer by application of a cross-linking agent in a separate step to the surface of the thermo-adhesive dots.
In U.S. Pat. No. 3,922,418, to Lauchenauer, an interlining material is disclosed having a cross-linking agent in contact only with the surfaces of the resin particles on a supporting fabric; the amount of cross-linking agent in the coating is insufficient to cross-link more than about 40% of the resin. Thus, a weaker bond results between adjoining fabric pieces, and the resin in contact with the supporting fabric which is not cross-linked may soften or melt at elevated temperatures, so that it is easier to break the bond between adjoining fabric pieces.
In U.S. Pat. No. 3,937,859, to Cara et al., a thermo-plastic and thermo-setting resin is formed of a cross-linking agent combined with a terpolymer having the following formula: EQU --[(R).sub.a --(CH.sub.2 C(Cl)H).sub.b (CH.sub.2 C(X)H).sub.c ].sub.n --
where R is selected from the group consisting of ethylene, propylene and butylene, and X is a radical selected from the group consisting of --CONH.sub.2 and --COOH. The ratio of a to b is about 1, and c is 1/20 of a and b combined.
The cross-linking agent is a urea formaldehyde, triazine formaldehyde, or melamine resin. The vinyl chloride mer gives off hydrogen chloride gas on heating, which is believed to act as a catalyst in the cross-linking reaction. A fabric, with the terpolymer/cross-linking agent composition thereon, is dried for 20-30 second at about 220.degree. F., which brings the resin to a temperature of about 150.degree. F. (approximately @ 65.degree. C.), at which point the resin softens and becomes adhesive. The fabric is then applied to an outer apparel fabric at a temperature of about 300.degree. F. (148.9.degree. C.). Thus, the adhesive resin used in Cara becomes thermo-adhesive at a relatively low temperature -65.degree. C., but does not become sufficiently cross-linked until a temperature of 150.degree. C. is reached; despite suggesting a temperature range of 250.degree. F. to 350.degree. F., Cara does not teach any compositions or make any suggestions which would enable one to sufficiently cross-link a thermo-adhesive at temperatures below 300.degree. F. (150.degree. C.); this high cross-link temperature required by Cara can damage heat sensitive fabrics. The required vinyl chloride mer of Cara produces HCl gas upon heating, so it can degrade the textile substrate (particularly substrates such as polyester and polyamide), and incomplete cross-linking can cause yellowing of the substrate. Further, it is well known that heating causes polyvinyl chloride to decompose, so it is believed that Cara's terpolymer will break down in high temperature laundering.
Thus, there remains a need for resins which can be stable at ambient temperatures, yet which can become sufficiently cross-linked at lower temperatures than the prior art adhesive formulations used in fabric interlinings. Lower thermo-set temperatures result in energy savings, cause less damage to fabrics which are heat sensitive, and use of resins which become thermo-adhesive at higher temperatures reduces the risk of inadvertent fusing of thermo-adhesive textile products to one another or to other materials prior to use.
Therefore, it is the primary object of the present invention to produce an improved thermo-adhesive cross-linkable textile product and methods for producing and using same in reinforcing other materials.
It is a further object of the present invention to provide an improved thermo-adhesive layer in a thermo-adhesive cross-linkable textile product which becomes tacky or adhesive at temperatures above 80.degree. C. and which cross-links at a temperature (critical temperature) above 100.degree. C., and preferably at about 120.degree. C. to about 130.degree. C.